Multiple petitions , H1 denial & out of status

[rajvar]

Hi , 

I have this specific scenario & could find an answer any where in the blog .

Employer A had petitioned for my H1 in 2015 cap , got it approved and stamped till 2018.

I didn't travel , instead got it transferred to employed B , who filed a cap exempted petition but got it only till 2017 .

With the visa stamping from employer A & i797 from both employers , I traveled , at POE no questions asked and got an i94 till 2018 based on A's petition .Now employer B has filed an extension . 
I have got a better offer from employer C , but with premium processing suspended I would have  to join with receipt number.B will have to inform USCIS that I have stopped working for them (this is mandatory , thats what i understand , please correct me if wrong.

Below are my questions around this scenario 

1. Is it a normal process to get an i94 based on the employer , whom I was not planning to work for ?
2. H1 extension & i94 extension , how are these two different .
3. If i join C on receipt notice , and if this gets denied , I would be out of status .but is the out of status counted from the day I stopped working for B or the day the C's petition got denied?
4. By the time C's petition is being processed , can D file another H1 transfer? Would this help as a back up to fall back in case C's petition get denied.
5. How would the out of status impact the future Green Card prospectus.

I understand its a complex question .With all the experience members please help me .